The present invention relates to an exposure apparatus and an exposing method for directly writing (drawing) and exposing a pattern on a photosensitive resin without using any of masks (in a mask-less manner), and a printed wiring board manufacturing method of manufacturing a printed wiring board by utilizing the exposing method.
In recent years, a requirement for low cost and/or high throughput production has been increased as multi-item and small-lot production of printed wiring boards has advanced.
In processing a pattern for a printed wiring board or the like in the prior art, various kinds of photosensitive resins called photo resists are used in various processes. More specifically, after a photosensitive liquid resist or dry film resist is coated on a board, the photosensitive liquid resist or dry film resist thus coated is exposed through a photo mask, and etching process, plating process and the like are performed after a developing process, thereby forming a predetermined pattern.
Instead of the pattern forming technique as described above, a mask-less direct exposing technique using a gas laser, such as an argon ion laser, for emitting visible light as a light source has been introduced since 1990s. This technique has such a feature that the cost of mask manufacture equipment and the material cost can be greatly saved and highly precise exposure can be made because the manufacture of the photo masks is unnecessary. Thus, this technique is expected as a technique for innovating manufacturing processes for a printed wiring board, a semiconductor package or the like.
In order to improve the maintenance performance for the gas laser in the mask-less direct exposing technique, it has been proposed to use a semiconductor laser diode not requiring supply of any of process gases as a light source. For example, JP-A 2004-85728 describes a method of directly exposing a photosensitive resin having specific composition containing an infrared absorbing coloring matter to a laser beam having a wavelength in the range of 750 to 1200 nm.
On the other hand, instead of the method of scanning a photosensitive resist with a laser beam reflected by a polygon mirror scanner, a direct exposing method using a digital micro mirror device (DMD) as an optical system having high generality is attracting the attention of the industry as an idea for improving the light applying method. The DMD is a spatial modulator including a reflecting mirror array which is integrated on a semiconductor chip by utilizing a micro machine technique. The reflecting mirrors operate at a high speed in accordance with digital information. The DMD is used as a DMD engine in combination with an optical system such as a micro lens array, a diffracting grating or the like. For example, JP-A 62-21220, JP-A 2004-157219, JP-A 2004-39871, etc. describe the mask-less exposing method using the DMD.
On the other hand, a technique for heating a substrate to increase sensitivity of a photo resist after exposure but before development is generally known in the art. For example, JP-A 2004-71624 describes an exposure apparatus including an exposing unit for irradiating a substrate having a photosensitive material applied thereon through a photo mask with light to expose the photosensitive material, and a baking unit for subjecting the substrate to heating processing after exposure but before development. Also, JP-A 2002-296402 provides a description in which an infrared ray lamp may be used for heating processing.